Objectives: To study acute exposure to imidazoline derivatives in 72 children younger than 15 years of age, followed-up from January 1994 to December 1999. Methods: This is a retrospective study of 72 patients with age between 2 months and 13 years (median 2 years; 25-75% = 1 to 3 years old) exposed to naphazoline (N=48), fenoxazoline (N=18), oxymetazoline (N=5) and tetrahydrozoline (N=1), through oral (N=46), nasal (N=24) or unknown (N=2) routes. Results: Fifty-seven children developed clinical manifestations such as somnolence (N=34/57), sweating (N=20/57), pallor (N=17/ 57), hypothermia (N=16/57), bradycardia (N=13/57), cool extremities (N=9/57), restlessness (N=7/57), tachycardia (N=6/57), vomiting (N= 5/57), irregular respiratory pattern and apnea (N= 5/57), miosis/ mydriasis (N=4/57). Naphazoline was the active ingredient most frequently involved (N=47), followed by phenoxazoline (N=5) and oxymetazoline (N=4). The onset of clinical manifestations was rapid, beginning within 2 hours after exposure in 32/57 children, Only supportive measures were employed, with one child requiring mechanical ventilation after accidental naphazoline ingestion. In most of the children resolution of symptoms occurred within 24 hours (N= 39/57). No deaths were observed. Patients exposed to naphazoline (N=47/48) presented a higher frequency of clinical signs of poisoning in comparison with those exposed to phenoxazoline (N=5/18) (p < 0.001). There were no significant differences in the frequency of patients who presented clinical manifestations considering the route of exposure [oral (N=34/46), nasal (N=21/24); p=0.31]. Conclusions: Most children (especially those younger than 3 years) exposed to imidazoline derivatives (especially naphazoline) presented early signs of poisoning regardless of the exposure route (nasal or oral). The main signs observed were nervous system, cardiovascular and respiratory depression. 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